Magnetic modulator



March 3, 1931. N. E. LINDENBLAD MAGNETIC MODULATOR Filed March 23, 1928 INVENTOR N BY 9 ATT I S E UNDENBLAD Patented Mar. 3, 1931 UNITE STATES PATENT OFFICE NILS E. LINDENBLLD, OF ROCKY POINT, NEW YORK, ASSIGNOR TO RADIO CORPORA- TION OF AMERICA, A CORPORATION OF DELAWARE MAGNETIC MODULATOR Application filed lllarch 23, 1928. Serial No. 264,131.

This invention relates to magnetic modulators I use the term magnetic modulator to mean saturable imepdances in general, that 5, is,'devices consisting essentially of a saturable core, a radio frequencywinding, and a modulator or low frequency or direct current winding for controlling the saturation of the core" To prevent the radio frequency energy from being induced into the saturation winding in such devices it has heretofore been proposed to construct two similar magnetic modulators, and to connect the radio frequency windings in series, in one sense, and

'15 the modulator windings in series, in the opposite sense, so that the radio frequency potential induced in the two modulator windings neutralize one another. It is an object of my invention to improve upon this arrangement,

which I do by the simple expedient of arranging the radio frequency and modulator windings relatively at right angles.

In order to make the device more eflicient it has been found advantageous to use a small diameter core. To provide such an arrange ment with windings which are not coupled to one another I make the core in the form of a slim tube, and thread the radio frequency winding through the tube, and wind the mod- 39 ulator winding around the tube. The opposite side of the radio frequency coil is preferably threaded through another similar small diameter tube of magnetic material,

which too is provided with a madulator winding. To form a closed magnetic circuit the two cores may be joined by yokes, and the modulator windings so connected in series that their flux flows additively around the magnetic circuit. Since the radio frequency flux flows around the tubes in circles concentric with the wires of the radio frequency winding, and the saturation flux flows along the tube, if it is desired to still further reduce eddy current losses the cylindrical cores 5 may be made up of a plurality of thin tubes arranged within one another. With less structural difiiculty the core may be made by rolling up a thin laminated strip, in which case the eddy current path is made as long as the spiral, but the flux must leap the gap between laminations at each revolution.

The invention is more fully described in thefollowing specificatiom'which is accom panied by a drawing in which Figure 1 is a schcmatic wiring diagram for my invention;

Figure 2 is a section. through a preferred form of magnetic modulator embodying my invention;

Figure 3 is a section taken on the line 3-3 in Figure 2; and

Figures land 5 are details explanatory of the construction of the core.

Referring to Figure 1 there is a supply circuit 2 which .is effective to feed energy to a utilization circuit 4 when the intermediate link circuit 6 is resonant to the working frequency. The intermediate circuit 6includes as a portion of its inductive reactance the radiofrequency coil 8, which is in juxtaposition to an iron core not shownon the diagram. Modulator windings '10 and 12 are wound at right angles to the conductors of the coil 8, so that the radio frequency energy is not transferredto the modulator circuit. The latter circuit includes a source of direct current 14 anda suitable modulating means, such as the key 16. When the keyis' closedthe resulting flow I of direct current saturates the core, greatly lessening the impedance of the coil 8, and thereby changing the tuning of the circuit 6. Preferably the circuit is brought into tune by closing'the key 16, so that energy is then transferred from circuit 2 to circuit 4.

The magnetic modulator is shown more in detail in Figure 2. in which in addition to radio frequency winding 8 and the modulator windings 10 and 12, there are shown the tubu lar cores 14 and 16. These are connected together by the yokes 18 and 20, so as to form a complete magnetic circuit. Between the radio frequency winding 8 and the cores 14 and 16 there are provided mica insulation tubes 22 and 24:. Similarly, between the modulator windings l0 and 12 and the cores 14 and 16 there are provided mica insulation tubes 26 and 28. These insulation tubes preferably are either fluted or additional spaced strips of bakelite are provided so that circulating spacing is left around the core. The

entire modulator may then be immersed in an oil bath 40 in a suitable container 42.

The cores 14 and 16 may be made of concentric laminations, instead of a single tube, and the yokes 18 and 20 are also laminated, as is indicated more clearly in Figure 3,

The core may also be made by rolling up a Hat sheet of magnetic material, rather than by using concentric tubes. In this case the eddy current path is made resistive because of its length, for it includes the entire length of the spiral strip 1 as indicated-in Figure 4. The potential causing eddy current flow depends on the height 0 of the rolled strip, and this may be subdivided, as has been indicated in Figure 2. This subdivision increases the reluctance of the direct current flux path, but not very much, and merely results in a slightly greater use of direct current. The high frequency flux path in each section of core requires a gradual passage through adjacent convolutions of the strip, as indicated in Figure 5, for the flux flow is in concentric circles and not in a spiral. The sacrifice in overall eflic'iency permits of much cheaper construction. 7 a

7 By the term magnetic modulator I include saturable impedances used for providing code or telephonic modulation, magnetic amplification, frequency multiplication, which are wellknown, and frequency modulation, a noveluse disclosed in a copending modulator windings are relatively at right angles and not coupled to one another.

4. A magnetic modulator comprising a saturable core including two tubes and two yokes of magnetic material forming a closed magnetic circuit, a radio frequency winding having its opposite sides threaded through said tubes, and modulator windings wound around each of the tubes and so connected in series that their flux flows additively around the magnetic circuit.

I 5. A magnetic modulator comprising a saturable core including two tubes and two yokes of suitably laminated magnetic material forming a closed magnetic circuit, a radio frequency winding having its opposite sides threaded through said tubes, and modulator windings wound around each of the tubes and so connected in series that their flux flows additively around the magnetic circuit. s

NILS E. LINDENBLAD.

application of Clarence 'W, Hansell, Serial No. 264,102'filedMarch 23,1928.

Iclaim: j i 1. A magnetic modulator comprising a saturable core including a pair of cylinders of magnetic material, a radiofrequency windin and a modulator winding, one of said windings being threaded through the cylinders of the core, and the other of said wind ings being wound around the cylinders of the L core, so that the two windings, while closely coupled to the core,-are not coupled to one another and means for maintaining the modulator immersed in a cooling fluid, V

2. A magnetic modulator comprising a saturable core including a pair of relatively small diameter tubes of magnetic material the tubes being long relative to their diameters,

a radio frequency winding threadedthrough the tubes, magnetic yokesfor the tubes, and

a modulator winding wound around the tube,

so that the two windings, while closely coupled to the core, are not coupled to'one another. 7 v V i 3. A magnetic .modulator comprisng a saturable core including two tubes, axially long relative to their diameters, of magnetic Vmaterial, magnetic yokes for joining the tubes, a radio frequency coil having its opposite sides threaded through, said tubes, and a-modulator winding wound around each lot the tubes, soithat the radiofreqnency and 

